An electrophotographic, monochrome image forming apparatus forms single color toner images on a photosensitive member. The toner images are transferred onto a sheet material passing through a nipping region defined between the photosensitive member and a transfer roller. Not all the toner particles are transferred onto the sheet material and a part of the toner particles remains on the photosensitive member without being transferred. In order to remove the residual toner particles from the photosensitive member, a method is proposed in which a cleaning member is provided in contact with the surface of the photosensitive member to remove the toner particles therefrom.
A variety of full color image forming apparatuses have been proposed so far. Among other things, one of the proposed electrophotographic, full color image forming apparatus is designed to transfer the toner images on the photosensitive member onto an intermediate transfer belt passing through a nipping region defined between the photosensitive member and a first transfer roller. The toner images are then transferred onto the sheet material passing through a second nipping region defined between the intermediate transfer belt and a second transfer roller. The residual toner particles on the intermediate transfer belt are removed by a cleaning member provided in contact with the photosensitive member.
Conventionally, the cleaning member for removing residual toner particles from the photosensitive member and the intermediate transfer belt is made of rubber blade in the form of elongate plate. Disadvantageously, the cleaning blade provides less cleaning ability for the spherical toner particles of smaller diameters.
To overcome this problem, JP 2004-310060 A discloses to use a rotatable cleaning brush for the cleaning member.
The cleaning device disclosed therein includes a cleaning brush mounted in contact with the outer peripheral surface of the intermediate transfer belt, and a charging brush mounted on the upstream side of the cleaning brush with respect to the rotational direction of the belt and in contact with the surface of the belt. According to the image forming apparatus, the untransferred toner particles are transported into the contact region of the belt and the charging brush by the rotation of the belt. As shown in FIG. 12, in the contact region the toner particles 100 are brought into contact with the bristles 176 of the brush 174 to have electric charge of normal polarity, for example, negative polarity. The charged toner particles are then transported into another contact region of the belt and the cleaning brush, where they are collected by the cleaning brush and removed from the peripheral surface of the belt.
In order for the untransferred toner particles to be completely removed from the belt, the toner particles are required to make good contacts with the charging brushes. For example, as shown in FIG. 13, the charging brush inappropriately forced against the belt may cause that a part of the toner particles 100 are transported through the contact region without any contact with the bristles 176 of the brush 174 when a large amount of toner particles 100 are transported into the region, which results in that the toner particles are not completely collected by the cleaning brush.